You're right of course. I just didn't understand what Cory was saying on the first and second round, but when he finally rephrased the statement I got it. Anyway, my style is not to do math to figure out what result I'll get from a lens. The old fashioned way of sticking it on the camera, looking through the finder, and making a few exposures seems to work pretty well for my needs.
Plus, there's something of a flaw in just using math to determine the AOV ... while a lens may be nominally rated at a particular focal length, it may not in actuality be that focal length. Depending on the actual focal length of the lens the difference may be significant. As a Leica user I'm sure you've noticed that Leica has the actual focal length coded on the barrel of some of their lenses. It seems that, apart from the nominal FL often being an approximation, variations in the build of each sample can be different as well. And, if you recall, not long ago Cotty put up some pics made with lenses of similar focal lengths that seemed to show a greater difference than would have been expected had the nominal FL of the lenses been precisely as indicated by the manufacturer. While it's nice to know how to figure out all these technical things, I feel that nothing beats making a photograph to get to the truth when it comes to lenses and all their characteristics. Shel > [Original Message] > From: Rob Studdert > On 23 Apr 2005 at 10:10, Shel Belinkoff wrote: > > > Too much math, not enough photography .... I don't understand the need for > > equations, nor do I understand the math, the equations, or your conclusion. > > > > Like I said, the field of view, regardless of your math, is greater with > > the Zenitar than it is with a 20mm lens on a 35mm camera. Have you looked > > through both focal lengths on a 35mm camera? Have you actually compared > > photos side-by-side? > > From a practical perspective you are of course correct Shel, the fisheye lens > will provide a wider AOV than the a rectilinear lens of equal focal length. > However due to the physics you will find that the fisheye effect diminishes as > the image is cropped (and this can be easily described in mathematical terms, > as Cory showed). So a 16mm fisheye on an APS sized DSLR frame looks far less > fishy than you might expect. > > Cory said: "So, what I *meant* to say is that FOV of the fisheye is about > equivalent to a 13-14mm rectilinear lens on the -DS, or a 20mm rectilinear > lens on a full-frame 35mm body." > > How I interpreted that paragraph was that a 16mm lens on a D or DS body > produces an angle of view roughly equivalent to the AOV a 20mm lens will > provide on a full frame 35mm body, and I agree.
